Plastic and Lateral-Torsional Buckling Behavior of Single Cold-Formed Channels Connected Back-to-Back

This paper describes the results of a series of experiments on semi-rigid and inelastic joints, and lateral-torsional buckling of the eaves region of portal frames comprising cold-formed single channels bolted back to back at the eaves and apex joints. The tests demonstrate the considerable ductility that is achieved in the back to back bolted connections, which should be sufficient in many cases to accommodate plastic analysis of the portal frames. Variables in the tests include the number of bolts in the connection, the lengths between lateral restraints, the width of the channel flanges, and the strength of the channels. Adjacent column and rafter channels are oriented successively in opposite transverse directions to take advantage of the counterbalancing moments and forces in the back to back connections. This system is important in enhancing the lateral buckling strength of the channels. An innovative method is proposed for connecting each purlin to the web of the column or rafter through a cold-formed angle. Experiments have shown this system to be capable of restraining the frames from failing due to lateral-torsional buckling. This eliminates the idea of having fly bracings, which is normally done in practice to restrain torsional instability.